Injection molding method and injection molding apparatus

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an injection molding method and injection molding apparatus in which a resin molded article is obtained by injection molding a resin material.

2. Related Art

For example, in a resin molded article manufacturing method in Japanese Patent No. 3,611,058, in molding a molded article having a partial thick wall on a rear surface side, it is designed to prevent a shrink from occurring on a front surface side of the molded article.

That is, in Japanese Patent No. 3,611,058, in a cavity of a forming mold for molding the molded article, a pressurized fluid inlet is formed on the same side as a rear surface side on which the thick wall is molded. Also, on the rear surface side of the cavity, a portion corresponding to a base of the thick wall is formed using a heat insulating material.

Then, a cooling of a resin in the proximity of the base of the thick wall is more delayed by the heat insulating material than a cooling of a resin on the periphery of the resin, and the base of the thick wall and the proximity of the base are pressed against the front surface side of the cavity from the rear surface side of the cavity by a pressurized fluid which has been injected from the inlet into an area between the rear surface side of the molded article and the heat insulating material, thus preventing a shrink from occurring on the front surface side of the molded article.

However, in the existing injection molding technique, particularly, when molding a large-size resin molded article or a resin molded article having a length which is larger than a thickness or a width, in the event that a plurality of the pressurized fluid inlets (gas inlets) is provided along a passage direction of the resin in the cavity, it is not designed to prevent a shrink and the like from occurring on the front surface side of the molded article.

That is, when carrying out an injection molding of the large-size or long resin molded article, a certain amount of time (a few seconds) is required to cause a molten resin to reach a distal end of the cavity from a resin inlet (a resin inlet gate) in the cavity. At this time, in the event that, in the same way as in the existing technique, an introduction of a gas into the cavity from the inlet is carried out after the molten resin has reached the distal end of the cavity, a surface skin (a cured portion) formed on a surface of the molten resin which makes contact with the mold tool has grown considerably in the proximity of the resin inlet, leading to a reduction in effectiveness in preventing the shrink and the like.

Further, there is a case that a boss of circular cross-section is projected from a rear surface of a plate-like body in a resin molded article used as various component parts of an automobile in order to attach the resin molded article to another component member, or for strengthening purposes.

As a method for manufacturing a resin molded article including such a boss, there is, for example, one disclosed in JP-A-10-86169 and JP-A-2005-28731.

JP-A-10-86169 discloses that, in injection molding a resin molded article, when a molten resin to be formed into the resin molded article is cooling and curing, a compressed gas is supplied to an inside of a boss, and a portion of the molten resin near a base of the boss is pressed against a mold tool by the compressed gas. Also, JP-A-2005-28731 discloses that, in manufacturing a resin molded article provided with a boss, a tubular pin and an inner pin are disposed in an inner portion of a cavity forming the boss, and, a compressed gas is supplied from a gap between the tubular pin and the inner pin, thereby pressing a molten resin which has filled an inside of a cavity.

Then, in JP-A-10-86169 and JP-A-2005-28731, a state of strain such as a shrink (a dimple formed on a surface) is prevented from occurring on a front surface of a plate-like body opposite a rear surface on which the boss stands.

However, even the existing resin molded article manufacturing method does not suffice for effectively preventing a state of strain such as a shrink from occurring on a front surface of the resin molded article having the boss.

That is, in the existing resin molded article manufacturing method, only an inner bottom of the boss is pressed by the compressed gas, so it is possible to prevent a shrink or the like from occurring on the front surface corresponding to an inner portion of the boss, but the manufacturing method does not suffice for preventing the shrink or the like from occurring on the front surface corresponding to an outer portion of the boss. Also, when causing the compressed gas to press only the inner bottom of the boss, in some situations, there is a possibility that the compressed gas enters an inside of the molten resin, and forms a hollow portion inside the resin molded article.

SUMMARY OF THE INVENTION

The invention, having been conceived with such an existing problem in mind, has an object of providing an injection molding method and injection molding apparatus which can effectively prevent a state of strain such as a shrink (a dimple formed on a surface) from occurring on a whole of a front surface of a resin molded article, including a surface corresponding to a boss formation position.

A first aspect of the invention provides an injection molding method using a forming mold provided with a cavity which is filled with a resin material to obtain a resin molded article and a resin inlet through which the resin material is introduced into the cavity, wherein a plurality of gas inlets through which a gas is introduced are formed on a rear molding surface of the cavity for molding a rear surface of the resin molded article, and the gas is introduced into an area between the rear molding surface and the resin material inside the cavity, the injection molding method including the steps of:

introducing the resin material into the cavity from the resin inlet; and,

pressing the resin material against a front molding surface of the cavity for molding a front surface of the resin molded article by introducing the gas to the gas inlets when the cavity is filled with the resin material, wherein a gas inlet positioned close to the resin inlet starts an introduction of the gas earlier than a gas inlet positioned far from the resin inlet.

In the injection molding method of this aspect of the invention, a forming mold provided with the plurality of gas inlets is used. Then, by devising a timing of ejecting the gas from each gas inlet, a state of strain such as a shrink is effectively prevented from occurring on the front surface of the resin molded article.

In injection molding the resin molded article, the resin material is introduced into the cavity from the resin inlet.

Then, when filling the inside of the cavity with the resin material, the gas inlet in a position inside the cavity which is close to the resin inlet (the gas inlet provided in an area inside the cavity which is first filled with the resin material) first starts the introduction of the gas into an area between the rear molding surface of the cavity and the resin material inside the cavity. By this configuration, the area inside the cavity which is first filled with the resin material first presses the resin material against the front molding surface of the cavity.

For that reason, in this aspect of the invention, a surface skin (a cured portion of the resin material) formed on a surface of a molten resin, which makes contact with a molding surface of the cavity, grows first in an area inside the cavity which is first filled with the resin material. At the same time, it is possible to first carry out the pressing of the resin material which has filled the area in which the surface skin grows first.

Therefore, according to the injection molding method of this aspect of the invention, it is possible to effectively prevent a state of strain such as a shrink (a dimple formed on a surface) from occurring on a whole of the front surface of the resin molded article.

A second aspect of the invention provides an injection molding method, using a forming mold provided with a cavity which is filled with a resin material to obtain a resin molded article and a resin inlet through which the resin material is introduced into the cavity, wherein one or a plurality of gas inlets through which a gas is introduced is formed on a rear molding surface of the cavity for molding a rear surface of the resin molded article and the gas is introduced into an area between the rear molding surface and the resin material inside the cavity, the injection molding method including the steps of:

introducing the resin material into the cavity from the resin inlet; and

pressing the resin material against a front molding surface of the cavity for molding a front surface of the resin molded article by starting introducing the gas from at least one of the gas inlets while the resin material is flowing into the cavity.

In the injection molding method of this aspect of the invention, when the resin material is flowing inside the cavity, the introduction of the gas is started from at least one gas inlet.

For that reason, in this aspect of the invention, it is possible to press the resin material against the front molding surface of the cavity before a surface skin (a cured portion of the resin material) formed on a surface of a molten resin, which makes contact with a molding surface of the cavity, grows too much.

Therefore, according to the injection molding method of this aspect of the invention too, it is possible to effectively prevent a state of strain such as a shrink (a dimple formed on a surface) from occurring on the whole of the front surface of the resin molded article.

A third aspect of the invention provides an injection molding apparatus, including:

a forming mold provided with a cavity which is filled with a resin material to obtain a resin molded article and a resin inlet through which the resin material is introduced into the cavity,

wherein, a gas inlet through which a gas is introduced is formed on a rear molding surface of the cavity for molding a rear surface of the resin molded article, and the gas is introduced into an area between the rear molding surface and the resin material inside the cavity,

a plurality of the gas inlets are provided along a passage direction of the resin material in the cavity, and wherein the apparatus is configured such that the resin material is introduced into the cavity from the resin inlet, and an introduction of the gas through the plurality of gas inlets is sequentially started, beginning with the gas inlet provided in an area inside the cavity which is first filled with the resin material.

The injection molding apparatus of this aspect of the invention, including a forming mold provided with the plurality of gas inlets, is configured such that the introduction of the gas through the plurality of gas inlets is sequentially started, beginning with the gas inlet provided in an area inside the cavity which is first filled with the resin material.

By this configuration, in this aspect of the invention too, the resin material can be pressed against the front molding surface of the cavity, in order, starting with the area inside the cavity which is first filled with the resin material. Then, it is possible to first carry out the pressing of the resin material which has filled the area in which the surface skin grows first.

Therefore, according to the injection molding method of this aspect of the invention, it is possible to effectively prevent a state of strain such as a shrink from occurring on the whole of the front surface of the resin molded article.

In the first to third aspects of the invention, the resin molded article can be a radiator grille, a back garnish, a side molding, a wheel cover, an instrument panel or the like. Also, the gas injected into the forming mold can be air or a high pressure gas such as nitrogen.

Also, before a whole of the inside of the cavity is filled with the resin material, the introduction of the gas through the gas inlets can be sequentially started, beginning with the gas inlet formed in an area inside the cavity which is first filled with the resin material. In this case, effectiveness is especially increased when a size of the resin molded article is relatively large, and a period of time to fill the inside of the cavity with the resin material is relatively long.

Also, the introduction of the gas through the gas inlets can also be started immediately after the resin material fills up to each relevant gas inlet formation position inside the cavity.

Also, the introduction of the gas through the gas inlets can also be started from any plurality of gas inlets at one time. In this case too, by staggering timings of starting the introduction of the gas into an area between any plurality of gas inlets and the remaining gas inlets, it is possible to obtain the same working effect as the heretofore described one.

Also, when carrying out the introduction of the gas through the plurality of gas inlets, preferably, the gas inlet having first started the introduction of the gas keeps introducing the gas even when another gas inlet subsequently starts the introduction of the gas. Then, it is preferable that the introduction of the gas from the plurality of gas inlets continues for a prescribed period of time after the whole of the cavity is filled with the resin material.

Also, in the first aspect of the invention, it is preferable that the resin molded article includes a plate-like body and a standing wall standing from a rear surface of the plate-like body, the cavity includes a body cavity for molding the plate-like body and a standing wall cavity for molding the standing wall, the body cavity is formed with a plurality of closed spaces which are areas surrounded by the standing wall cavity, and a plurality of the gas inlets is provided corresponding to portions of the rear molding surface in the plurality of closed spaces, and that the resin material is introduced into the cavity from the resin inlet and, when filling an inside of each of the closed spaces with the relevant resin material, a gas inlet provided in the closed space positioned close to the resin inlet starts the introduction of the gas earlier than a gas inlet provided in the closed space positioned far from the resin inlet.

Also, in the third aspect of the invention, it is preferable that the resin molded article includes a plate-like body and a standing wall standing from a rear surface of the plate-like body, the cavity includes a body cavity for molding the plate-like body and a standing wall cavity for molding the standing wall, the body cavity is formed with a plurality of closed spaces which are areas surrounded by the standing wall cavity, and a plurality of the gas inlets is provided corresponding to portions of the rear molding surface in the plurality of closed spaces, and that the apparatus is configured such that the resin material is introduced into the cavity from the resin inlet and, when filling an inside of each of the closed spaces with the relevant resin material, the introduction of the gas is sequentially started, beginning with the gas inlet provided in the closed space which is first filled with the relevant resin material.

In these cases, the resin molded article having the standing wall standing from the rear surface of the plate-like body can be molded with a state of strain such as a shrink effectively prevented from occurring on a whole of the front surface. That is, by the gas inlet being provided in each closed space, it is possible to press the resin material, which has filled the inside of the cavity, against the front molding surface of the cavity. For that reason, it is possible to carry out the pressing of the resin material by the gas before the surface skin grows too much inside the closed space first filled with the resin material, making it possible to effectively prevent a state of strain such as a shrink from occurring.

Also, when carrying out the introduction of the gas, a gas, which has been introduced from a gas inlet into an area between the rear molding surface in a closed space and the resin material which has filled the closed space, can be prevented, by the resin material having filled the inside of the standing wall cavity, from reaching an area between the rear molding surface in adjacent closed spaces and the resin material which has filled the inside of the closed spaces.

Also, in the first aspect of the invention, it is possible that the introduction of the gas through the gas inlets is started after an inside of at least one of the closed spaces is filled with the resin material and before a whole of the cavity is filled with the relevant resin material.

In this case, it becomes easy to press the relevant resin material against the front molding surface of the cavity before the surface skin grows too much inside the cavity.

Also, in the second aspect of the invention, it is preferable that the resin molded article includes a plate-like body and a standing wall standing from a rear surface of the plate-like body, the cavity includes a body cavity for molding the plate-like body and a standing wall cavity for molding the standing wall, the body cavity has formed in a portion thereof a closed space which is an area surrounded by the standing wall cavity, and the gas inlet is provided corresponding to the rear molding surface in the closed space, and that the introduction of the gas is started after the resin material flowing inside the cavity fills the closed space and before a whole of the cavity is filled with the relevant resin material.

In this case too, it becomes easy to press the relevant resin material against the front molding surface of the cavity before the surface skin grows too much inside the cavity.

Also, in the second aspect of the invention, it is also possible that the resin molded article includes a plate-like body and a standing wall standing from a rear surface of the plate-like body, the cavity includes a body cavity for molding the plate-like body and a standing wall cavity for molding the standing wall, the body cavity is formed with a plurality of closed spaces which are areas surrounded by the standing wall cavity, and a plurality of the gas inlets is provided corresponding to portions of the rear molding surface in the plurality of closed spaces, and that the introduction of the gas is started after the resin material flowing inside the cavity fills one of the closed spaces and before the whole of the cavity is filled with the relevant resin material.

In this case too, it becomes easy to press the relevant resin material against the front molding surface of the cavity before the surface skin grows too much inside the cavity.

Also, in the third aspect of the invention, it is preferable that the apparatus is configured such that the introduction of the gas through the gas inlet is started after the resin material fills the inside of the closed space provided with the relevant gas inlet and before the relevant resin material fills the inside of the next closed space.

In this case, the introduction of the gas from the gas inlet can be started each time the inside of each closed space is filled with the resin material. By this configuration, by pressing the resin material, which has filled the inside of the cavity for each closed space, against the front molding surface of the cavity, and carrying out the pressing of the resin material by the gas before the surface skin grows too much, it is possible to effectively prevent a state of strain such as a shrink from occurring on the whole of the front surface of the resin molded article.

Also, in the third aspect of the invention, it is preferable that the apparatus is configured such that the introduction of the gas through the gas inlets is sequentially started, beginning with the gas inlet located in an area having a short passageway length of the resin material from the resin inlet.

In this case, the introduction of the gas can be carried out in accordance with an order in which the resin material passes through each area inside the cavity.

Also, an area or a closed space which is first filled with the resin material can be an area or a closed space having a short resin material passageway length from the resin inlet.

Also, in the first to third aspects of the invention, the introduction of the gas through the gas inlet can be started immediately after the resin material fills the inside of the closed space provided with the relevant gas inlet. In this case, after an inside of a closed space is filled with the resin material, the introduction of the gas can be swiftly started before the surface skin grows too much inside the closed space.

Also, a status of a flow of the resin material inside the cavity can be monitored by a sensor provided in the forming mold. Then, the sensor detects that an inside of a closed space has been filled with the resin material and, when the detection occurs, the introduction of the gas can be started from the gas inlet provided in the closed space.

Also, under prescribed injection molding conditions, when a time at which the resin material fills the inside of each closed space is known, the introduction of the gas from each gas inlet can be started after the introduction of the resin material into the cavity from the resin inlet is started and a prescribed period of time has elapsed.

A fourth aspect of the invention provides a resin molded article manufacturing method for manufacturing a resin molded article including a boss of circular cross-section projected from a rear surface of a plate-like body, using a forming mold formed with a body cavity for molding the plate-like body and a boss cavity for molding the boss; the forming mold including an inner gas nozzle provided inside an inner molding wall of the boss for forming an inner periphery of the boss cavity, and an outer gas nozzle provided in a rear molding surface of the body cavity for molding a rear surface of the plate-like body, the method including:

filling an inside of the body cavity and boss cavity with a resin material,

pressing the resin material against a front molding surface of the body cavity for molding a front surface of the plate-like body by injecting a gas from the outer gas nozzle into an area between the rear molding surface and the resin material which has filled the inside of the body cavity; and

pressing the resin material against the front molding surface by injecting the gas from the inner gas nozzle into an area between a leading end surface of the inner molding wall and the resin material facing the leading end surface.

In the resin molded article manufacturing method of this aspect of the invention, a forming mold provided with the inner gas nozzle and the outer gas nozzle is used. Then, by devising a timing of ejecting the gas from the inner gas nozzle and the outer gas nozzle, a state of strain such as a shrink is effectively prevented from occurring on a front surface of the resin material.

In manufacturing the resin molded article, first, the inside of the body cavity and boss cavity is filled with the resin material. At this time, a filling of the boss cavity with the resin material can be carried out via the body cavity.

Next, the gas is injected from the outer gas nozzle into the area between the rear molding surface of the body cavity and the resin material which has filled the inside of the body cavity. At this time, the resin material inside the body cavity is pressed against the front molding surface of the body cavity.

Next, the gas is injected from the inner gas nozzle into the area between the leading end surface of the inner molding wall and the resin material facing the leading end surface. At this time, the resin material inside the body cavity is pressed against the front molding surface of the body cavity.

By this configuration, in this aspect of the invention, in a condition in which the resin material positioned in the proximity of an outer periphery of the boss cavity is pressed against the front molding surface of the body cavity, the resin material facing the leading end surface of the inner molding wall (the resin material positioned on an inner peripheral side of the boss cavity) can be pressed against the front molding surface of the body cavity.

Therefore, in the resin molded article molded by the manufacturing method of this aspect of the invention, it is possible to effectively prevent a state of strain such as a shrink (a dimple formed on a surface) from occurring on the front surface corresponding to the whole of the boss formation position.

A fifth aspect of the invention provides a resin molded article manufacturing apparatus for manufacturing a resin molded article including a boss of circular cross-section projected from a rear surface of a plate-like body, the apparatus including:

a forming mold formed with a body cavity for molding the plate-like body and a boss cavity for molding the boss;

an inner gas nozzle provided inside an inner molding wall forming an inner periphery of the boss cavity; and

an outer gas nozzle provided in a rear molding surface of the body cavity for molding a rear surface of the plate-like body,

wherein the apparatus is configured such that, a gas is injected through the inner gas nozzle into an area between a leading end surface of the inner molding wall and the resin material facing the leading end surface, after a gas is injected through the outer gas nozzle into an area between the rear molding surface and the resin material which has filled the inside of the body cavity.

The resin molded article manufacturing apparatus of this aspect of the invention, including a forming mold provided with the inner gas nozzle and the outer gas nozzle, is configured such that, after the gas is injected through the outer gas nozzle into the area between the rear molding surface of the body cavity and the resin material which has filled the inside of the body cavity, the gas is injected through the inner gas nozzle into the area between the leading end surface of the inner molding wall and the resin material facing the leading end surface.

By this configuration, in this aspect of the invention too, in a condition in which the resin material positioned farther to the outer peripheral side than the boss cavity is pressed against the front molding surface of the body cavity, the resin material facing the leading end surface of the inner molding wall (the resin material positioned on an inner peripheral side of the boss cavity) can be pressed against the front molding surface of the body cavity.

Therefore, in the resin molded article molded by the manufacturing apparatus of this aspect of the invention, it is possible to effectively prevent a state of strain such as the shrink from occurring on the front surface corresponding to the whole of the boss formation position.

The fourth and fifth aspects of the invention relate to a method and apparatus for manufacturing a resin molded article including a boss of circular cross-section projected from a rear surface of a plate-like body.

In the fourth and fifth aspects of the invention, the resin molded article can be a radiator grille, a back garnish, a side molding, a wheel cover, an instrument panel or the like.

Also, the boss can be used as an attachment portion used for attaching the resin molded article to another part. In the case of using the boss as the attachment portion, for example, it is possible that a threaded hole is formed on an inner periphery of the boss, and a screw disposed on the another part is screwed into the threaded hole.

Also, the plate-like body is not necessarily formed as a whole of the resin molded article, as it can also be formed as one portion of the resin molded article. In the case of forming the plate-like body as one portion of the resin molded article, as will be described hereafter, it is preferable that the plate-like body is formed surrounded by a projecting wall projecting from the rear surface thereof.

Also, the gas injected into the forming mold can be a high pressure gas such as air.

A timing of starting the injection of the gas into the forming mold from the inner gas nozzle can be after the gas injected from the outer gas nozzle spreads all over a perimeter of the body cavity on the outer peripheral side. Also, a timing of starting the injection of the gas into the forming mold from the inner gas nozzle can also be after the gas spreads into a whole of the area between the rear molding surface of the body cavity and the resin material which has filled the inside of the body cavity.

Also, in the fourth aspect of the invention, it is preferable that the plate-like body is surrounded by a projecting wall projecting from the rear surface thereof, a projecting wall cavity for molding the projecting wall is formed contiguously with the body cavity, and, when filling the inside of the body cavity with the resin material, an inside of the projecting wall cavity is also filled with the relevant resin material. Also, in the fifth aspect of the invention, it is preferable that the plate-like body is surrounded by a projecting wall projecting from the rear surface thereof, and a projecting wall cavity for molding the projecting wall is formed contiguously with the body cavity.

In these cases, the gas injected from the outer gas nozzle into the area between the rear molding surface of the body cavity and the resin material which has filled the inside of the body cavity can be easily prevented, by the resin material having filled the inside of the projecting wall cavity, from reaching the front molding surface of the body cavity.

Also, in the fourth aspect of the invention, it is preferable that a rib cavity for forming a strengthening rib at a base of the boss is formed at a base of an outer periphery of the boss cavity, and, when filling the inside of the body cavity and boss cavity with the resin material, an inside of the rib cavity is also filled with the relevant resin material. Also, in the fifth aspect of the invention, it is preferable that a rib cavity for molding a strengthening rib at a base of the boss is formed at a base of an outer periphery of the boss cavity.

In these cases, in the resin molded article molded, the base of the boss can be strengthened by the strengthening rib.

BRIEF DESCRIPTION OF THE DRAWINGS

<figref idrefs="DRAWINGS">FIG. 1</figref> is a perspective view showing a resin molded article, according to a first embodiment;

<figref idrefs="DRAWINGS">FIG. 2</figref> is a plan view showing a formation of a cavity in a forming mold of an injection molding apparatus, according to the first embodiment;

<figref idrefs="DRAWINGS">FIG. 3</figref> is a sectional view showing the injection molding apparatus, looking in a direction of arrow A in <figref idrefs="DRAWINGS">FIG. 2</figref>, according to the first embodiment;

<figref idrefs="DRAWINGS">FIG. 4</figref> is a plan view showing the cavity in a condition in which an inside of central closed spaces is filled with a resin material, and a gas is introduced from gas inlets provided in the central closed spaces, according to the first embodiment;

<figref idrefs="DRAWINGS">FIG. 5</figref> is a sectional view showing the injection molding apparatus, looking in a direction of arrow A in <figref idrefs="DRAWINGS">FIG. 4</figref>, according to the first embodiment;

<figref idrefs="DRAWINGS">FIG. 6</figref> is a plan view showing the cavity in a condition in which an inside of intermediate closed spaces is filled with the resin material, and the gas is introduced from gas inlets provided in the intermediate closed spaces, according to the first embodiment;

<figref idrefs="DRAWINGS">FIG. 7</figref> is a sectional view showing the injection molding apparatus, looking in a direction of arrow A in <figref idrefs="DRAWINGS">FIG. 6</figref>, according to the first embodiment;

<figref idrefs="DRAWINGS">FIG. 8</figref> is a plan view showing the cavity in a condition in which an inside of distal closed spaces is filled with the resin material, and the gas is introduced from gas inlets provided in the distal closed spaces, according to the first embodiment;

<figref idrefs="DRAWINGS">FIG. 9</figref> is a sectional view showing the injection molding apparatus, looking in a direction of arrow A in <figref idrefs="DRAWINGS">FIG. 8</figref>, according to the first embodiment;

<figref idrefs="DRAWINGS">FIG. 10</figref> is a perspective view showing a resin molded article, according to a second embodiment;

<figref idrefs="DRAWINGS">FIG. 11</figref> is a sectional view showing a resin molded article manufacturing apparatus, according to the second embodiment;

<figref idrefs="DRAWINGS">FIG. 12</figref> is a sectional view showing the resin molded article manufacturing apparatus in a condition in which an inside of a forming mold is filled with a resin material, according to the second embodiment;

<figref idrefs="DRAWINGS">FIG. 13</figref> is a sectional view showing the resin molded article manufacturing apparatus in a condition in which a gas is injected into the forming mold from an outer gas nozzle, according to the second embodiment;

<figref idrefs="DRAWINGS">FIG. 14</figref> is a sectional view showing the resin molded article manufacturing apparatus in a condition in which the gas is injected into the forming mold from an inner gas nozzle, according to the second embodiment;

<figref idrefs="DRAWINGS">FIG. 15</figref> is a perspective view showing another resin molded article, according to the second embodiment;

<figref idrefs="DRAWINGS">FIG. 16</figref> is a sectional view showing the manufacturing apparatus in a condition in which the gas is injected from only the inner gas nozzle, and a shrink has occurred, according to a comparative example 1;

<figref idrefs="DRAWINGS">FIG. 17</figref> is a sectional view showing the manufacturing apparatus in a condition in which the gas is injected from only the inner gas nozzle, and a hollow portion has been formed, according to the comparative example 1; and

<figref idrefs="DRAWINGS">FIG. 18</figref> is a sectional view showing the manufacturing apparatus in a condition in which the gas is injected from only the outer gas nozzle, and the shrink has occurred, according to a comparative example 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

Hereafter, a description will be given, along with the drawings, of a first embodiment related to the injection molding method and the injection molding apparatus of the invention.

As shown in <figref idrefs="DRAWINGS">FIGS. 1 to 3</figref>, an injection molding method and an injection molding apparatus <b>1</b> of the first embodiment use a forming mold <b>2</b> provided with a plurality of gas inlets <b>4</b>A, <b>4</b>B, and <b>4</b>C for introducing a gas G which presses a resin material <b>80</b> inside a cavity <b>20</b>. Then, by devising a timing of ejecting the gas G from the gas inlets <b>4</b>A, <b>4</b>B, and <b>4</b>C, a state of strain such as a shrink, or shrink mark, is effectively prevented from occurring on a front surface <b>801</b> of a resin molded article <b>8</b>.

As shown in <figref idrefs="DRAWINGS">FIGS. 2 and 3</figref>, the injection molding apparatus <b>1</b> of the first embodiment includes a forming mold <b>2</b> provided with: a cavity <b>20</b> which is filled with a resin material <b>80</b> to obtain a resin molded article <b>8</b>; and a resin inlet <b>23</b> through which the resin material <b>80</b> is introduced into the cavity <b>20</b>.

A rear molding surface <b>202</b> of the cavity <b>20</b> for molding a rear surface <b>802</b> of the resin molded article <b>8</b>, is provided with the gas inlets <b>4</b>A, <b>4</b>B, and <b>4</b>C through which the gas G is introduced into an area between the rear molding surface <b>202</b> and the resin material <b>80</b> inside the cavity <b>20</b>. The plurality of the gas inlets <b>4</b>A, <b>4</b>B, and <b>4</b>C is provided along a passage direction L of the resin material <b>80</b> in the cavity <b>20</b>.

In molding the resin molded article <b>8</b> using the injection molding apparatus <b>1</b>, as shown in <figref idrefs="DRAWINGS">FIGS. 4 to 9</figref>, a molten resin material <b>80</b> is introduced into the cavity <b>20</b> from the resin inlet <b>23</b>. Then, when filling the inside of the cavity <b>20</b> with the resin material <b>80</b>, a gas inlet <b>4</b>A positioned close to the resin inlet <b>23</b> starts the introduction of the gas G earlier than a gas inlet <b>4</b>B, <b>4</b>C positioned far from the resin inlet <b>23</b>. In the first embodiment, the introduction of the gas G is sequentially started, beginning with a gas inlet <b>4</b>A provided in an area inside the cavity <b>20</b> which is first filled with the resin material <b>80</b>. By this configuration, the resin material <b>80</b> is sequentially pressed against a front molding surface <b>201</b> inside the cavity <b>20</b> for molding the front surface <b>801</b> of the resin molded article <b>8</b>, beginning with the area inside the cavity <b>20</b> which is first filled with the resin material <b>80</b>.

Hereafter, a detailed description will be given, along with <figref idrefs="DRAWINGS">FIGS. 1 to 9</figref>, of the injection molding method and injection molding apparatus <b>1</b> of the first embodiment.

As shown in <figref idrefs="DRAWINGS">FIG. 1</figref>, the resin molded article <b>8</b> molded in the first embodiment includes a plate-like body <b>81</b> and a standing wall <b>82</b> standing from the rear surface <b>802</b> of the plate-like body <b>81</b>. Also, a boss <b>812</b> for use in attaching the resin molded article <b>8</b> to another part or the like is formed projecting from the rear surface <b>802</b> of the plate-like body <b>81</b>. The boss <b>812</b> has a circular shape in cross-section. Then, a threaded hole into which is screwed a screw disposed on another part can be formed in an inner periphery of the boss <b>812</b> in an injection-molded resin molded article <b>8</b>.

The standing wall <b>82</b> in the first embodiment includes an outer peripheral standing wall <b>821</b> standing from an edge of the rear surface <b>802</b> of the plate-like body <b>81</b> and a partition standing wall <b>822</b> standing from the rear surface <b>802</b> of the plate-like body <b>81</b>. The resin molded article <b>8</b> of the first embodiment is a radiator grille. The partition standing wall <b>822</b> of the first embodiment, being a strengthening rib for strengthening the resin molded article <b>8</b>, is formed perpendicularly to a lengthwise direction (a right-left direction) W of the radiator grille.

As shown in <figref idrefs="DRAWINGS">FIG. 1</figref>, the plate-like body <b>81</b> of the first embodiment includes a plurality of body components <b>811</b>, which is elongated in the right-left direction W, formed in parallel and connected at right and left ends of the plate-like body <b>81</b>. The outer peripheral standing wall <b>821</b> of the first embodiment is formed on each side of the body components <b>811</b> in an up-down direction H, and the partition standing walls <b>822</b> are formed, standing from the rear surface <b>802</b> of each body component <b>811</b>, in a plurality of portions thereof in the right-left direction W.

As shown in <figref idrefs="DRAWINGS">FIGS. 2 and 3</figref>, the cavity <b>20</b> of the first embodiment includes a body cavity <b>21</b> for molding the plate-like body <b>81</b>, a standing wall cavity <b>22</b> for molding the standing wall <b>82</b>, and a boss cavity <b>212</b> for molding the boss <b>812</b>. Also, the body cavity <b>21</b> includes formed therein a plurality of closed spaces <b>3</b> which are areas surrounded by the standing wall cavity <b>22</b>.

The body cavity <b>21</b> of the first embodiment includes a plurality of cavity components <b>211</b> which mold the body components <b>811</b>. Also, the standing wall cavity <b>22</b> includes an outer peripheral standing wall cavity <b>221</b> for molding the outer peripheral standing wall <b>821</b> and partition standing wall cavities <b>222</b> for molding the partition standing walls <b>822</b>.

As shown in <figref idrefs="DRAWINGS">FIGS. 2 and 3</figref>, the closed space <b>3</b> of the first embodiment is formed as an area surrounded by the outer peripheral standing wall cavity <b>221</b> and the partition standing wall cavities <b>222</b>. A plurality of the closed spaces <b>3</b> is formed in the right-left direction W of the cavity <b>20</b>. The closed spaces <b>3</b> of the first embodiment include a central closed space <b>31</b> positioned in a center of the body cavity <b>21</b>, a distal closed space <b>33</b> positioned at each end of the body cavity <b>21</b> in the right-left direction W, and an intermediate closed space <b>32</b> formed between the central closed space <b>31</b> and the distal closed space <b>33</b>.

Also, a plurality of the central closed spaces <b>31</b> and the intermediate closed spaces <b>32</b> is formed on the right and left sides of the body cavity <b>21</b> in such a way as to correspond to the plurality of cavity components <b>211</b>.

Also, a plurality of the boss cavities <b>212</b> of the first embodiment is formed in each distal closed space <b>33</b>.

Also, a passageway length of the resin material <b>80</b> from the resin inlets <b>23</b> increases in an order of the central closed space <b>31</b>, the intermediate closed spaces <b>32</b> and the distal closed space <b>33</b>.

Also, as shown in <figref idrefs="DRAWINGS">FIGS. 2 and 3</figref>, the resin inlet <b>23</b> of the first embodiment is provided in a central portion of the cavity <b>20</b>, and the cavity <b>20</b> of the first embodiment is filled with the resin material <b>80</b>, which has been introduced from the resin inlet <b>23</b>, caused to diverge in the right-left direction W. Also, the resin inlet <b>23</b> of the first embodiment is provided in each of the plurality of cavity components <b>211</b>, and flows of the resin material <b>80</b> introduced into the individual cavity components <b>211</b> from the corresponding resin inlets <b>23</b> converge at ends of the cavity <b>20</b> in the right-left direction W.

The gas inlets <b>4</b>A, <b>4</b>B, and <b>4</b>C are provided in portions of the rear molding surface <b>202</b> in the corresponding closed spaces <b>3</b>. In the first embodiment, one gas inlet <b>4</b>A, <b>4</b>B is formed in each of the central closed spaces <b>31</b> and the intermediate closed spaces <b>32</b>, and a plurality of the gas inlets <b>4</b>C is formed in each distal closed space <b>33</b>.

Each gas inlet <b>4</b>A, <b>4</b>B, and <b>4</b>C includes a gap <b>43</b>, through which the gas G is caused to pass, formed between a gas passage hole <b>41</b> formed in the rear molding surface <b>202</b> of the cavity <b>20</b> and a cylindrical body <b>42</b> disposed inside the gas passage hole <b>41</b>.

The injection molding apparatus <b>1</b> of the first embodiment being for injection molding the resin molded article <b>8</b>, an injection pressure of the resin material <b>80</b> injected into the forming mold <b>2</b> is set at, for example, 30 to 50 MPa, and a heating temperature of the resin material <b>80</b> injected into the forming mold <b>2</b> is set at, for example, 200 to 250° C. Also, the gas G introduced into the cavity <b>20</b> from each gas inlet <b>4</b>A, <b>4</b>B, and <b>4</b>C is a high pressure gas of 5 to 15 MPa.

Although not shown, each gas inlet <b>4</b>A, <b>4</b>B, and <b>4</b>C is configured such that the gas G is ejected from it and the ejection is interrupted by means of a valve which opens and closes a flow channel of the gas G. Also, a timing of the gas G ejection from each gas inlet <b>4</b>A, <b>4</b>B, and <b>4</b>C can be controlled by control means such as a sequencer (a programmable controller).

Then, the control means in the injection molding apparatus <b>1</b> is configured such that, when sequentially filling the inside of the closed spaces <b>3</b> with the resin material <b>80</b> introduced into the cavity <b>20</b> from the resin inlets <b>23</b>, the introduction of the gas G is sequentially started, beginning with a gas inlet <b>4</b>A formed in a closed space <b>3</b> first filled with the relevant resin material <b>80</b>. More specifically, the control means of the first embodiment is configured such that the gas G is introduced from gas inlets <b>4</b>A, <b>4</b>B, and <b>4</b>C each time the closed spaces <b>3</b> are filled with the resin material <b>80</b>, in order, starting with the closed spaces <b>3</b> located close to the resin inlets <b>23</b>, that is, the central closed spaces <b>31</b>, the intermediate closed spaces <b>32</b> and the distal closed spaces <b>33</b> are filled with the resin material <b>80</b>, in the order named.

Next, a detailed description will further be given of a method for molding the resin molded article <b>8</b> using the injection molding apparatus <b>1</b>.

On injection molding the resin molded article <b>8</b>, as shown in <figref idrefs="DRAWINGS">FIGS. 4 and 5</figref>, the molten resin material <b>80</b> is introduced into each cavity component <b>211</b> of the cavity <b>20</b> from the plurality of resin inlets <b>23</b>. At this time, the resin material <b>80</b> flows from each resin inlet <b>23</b> toward the right and left of each cavity component <b>211</b>.

Then, as shown in the same figures, when the inside of the central closed space <b>31</b>, and the inside of the standing wall cavity <b>22</b> positioned around the central closed space <b>31</b>, in each cavity component <b>211</b>, are filled with the resin material <b>80</b>, that is, when a flow leading end <b>80</b>A of the resin material <b>80</b> fills up to the inside of first partition standing wall cavities <b>222</b>A, the control means starts the introduction of the gas G from a gas inlet <b>4</b>A provided in the central closed space <b>31</b>.

At this time, while the resin material <b>80</b> is flowing inside the cavity <b>20</b>, the gas G is injected into an area between the rear molding surface <b>202</b> in the central closed space <b>31</b> and the resin material <b>80</b> inside the central closed space <b>31</b>, and the resin material <b>80</b> is pressed against the front molding surface <b>201</b> in the central closed space <b>31</b>.

Also, the gas G introduced from the gas inlet <b>4</b>A provided in the central closed space <b>31</b> is prevented, by the resin material <b>80</b> having filled the inside of the first standing wall cavities <b>222</b>A, from reaching the inside of the intermediate closed spaces <b>32</b> adjacent to the central closed space <b>31</b>.

To continue, as shown in <figref idrefs="DRAWINGS">FIGS. 6 and 7</figref>, when the inside of the intermediate closed spaces <b>32</b>, and the inside of the standing wall cavity <b>22</b> positioned around the intermediate closed spaces <b>32</b>, in each cavity component <b>211</b>, are filled with the resin material <b>80</b>, that is, when the flow leading end of the resin material <b>80</b> fills up to the inside of second partition standing wall cavities <b>222</b>B, the control means starts the introduction of the gas G from gas inlets <b>4</b>B provided in the intermediate closed spaces <b>32</b>.

At this time, while the resin material <b>80</b> is flowing inside the cavity <b>20</b>, the gas G is injected into areas between the rear molding surface <b>202</b> in the intermediate closed space <b>32</b> and the resin material <b>80</b> inside the intermediate closed space <b>32</b>, and this resin material <b>80</b> is pressed against the front molding surface <b>201</b> in the intermediate closed spaces <b>32</b>.

Also, the gas G introduced from the gas inlets <b>4</b>B provided in the intermediate closed spaces <b>32</b> is prevented, by the resin material <b>80</b> having filled the inside of the second standing wall cavities <b>222</b>B, from reaching the inside of the distal closed spaces <b>33</b> adjacent to the intermediate closed spaces <b>32</b>.

To continue, as shown in <figref idrefs="DRAWINGS">FIGS. 8 and 9</figref>, when the inside of the distal closed spaces <b>33</b>, the inside of the standing wall cavity <b>22</b> positioned around the distal closed spaces <b>33</b>, and the inside of the boss cavities <b>212</b>, are filled with the resin material <b>80</b>, that is, when the resin material <b>80</b> fills a whole of the cavity <b>20</b>, the control means starts the introduction of the gas G from gas inlets <b>4</b>C provided in the distal closed spaces <b>33</b>.

At this time, the gas G is injected into areas between the rear molding surface <b>202</b> in the distal closed space <b>33</b> and the resin material <b>80</b> inside the distal closed space <b>33</b>, and this resin material <b>80</b> is pressed against the front molding surface <b>201</b> in the distal closed spaces <b>33</b>.

When introducing the gas G into the intermediate closed spaces <b>32</b>, the introduction of the gas G into the central closed spaces <b>31</b> is maintained and, when introducing the gas G into the distal closed spaces <b>33</b>, the introduction of the gas G into the central closed spaces <b>31</b> and the intermediate closed spaces <b>32</b> is maintained. Then, after the whole of the cavity <b>20</b> is filled with the resin material <b>80</b>, a condition in which the resin material <b>80</b> in all the closed spaces <b>3</b> is pressed against the front molding surface <b>201</b> by the gas G injected from all the gas inlets <b>4</b>A, <b>4</b>B and <b>4</b>C is maintained for a prescribed period of time, and the resin material <b>80</b> is cooled and cured, thereby forming the resin molded article <b>8</b>.

In this way, in the first embodiment, when filling the inside of the cavity <b>20</b> with the resin material <b>80</b>, inside the cavity <b>20</b>, the gas inlets <b>4</b>A and <b>4</b>B, provided in the closed spaces <b>3</b> first filled with the resin material <b>80</b>, first start the introduction of the gas G into the area between the rear molding surface <b>202</b> of the cavity <b>20</b> and the resin material <b>80</b> inside the cavity <b>20</b>. By this configuration, the resin material <b>80</b> is pressed against the front molding surface <b>201</b> of the cavity <b>20</b>, in order, starting with closed spaces <b>3</b> inside the cavity <b>20</b> which are first filled with the resin material <b>80</b>.

For that reason, in the first embodiment, a surface skin (a cured portion of the resin material <b>80</b>), which is formed on a surface of a molten resin which makes contact with molding surfaces (the front molding surface <b>201</b> and the rear molding surface <b>202</b>) of the cavity <b>20</b>, grows first in the closed spaces <b>3</b> which are first filled with the resin material <b>80</b> inside the cavity <b>20</b>. At the same time, the heretofore described pressing can be sequentially carried out, starting with the resin material <b>80</b> which has filled the closed spaces <b>3</b>, on which the surface skin grows first.

Then, inside the closed spaces <b>3</b> first filled with the resin material <b>80</b>, it is possible to carry out the heretofore described pressing of the resin material <b>80</b> by the gas G before the surface skin grows too much, making it possible to effectively prevent a state of strain such as a shrink from occurring.

Also, when the partition standing walls (the strengthening ribs) <b>822</b> are formed on the rear surface <b>802</b> of the resin molded article <b>8</b>, a state of strain such as a shrink easily occurs on the front surface <b>801</b> corresponding to partition standing wall <b>822</b> formation positions. In response, as described heretofore, by sequentially pressing the resin material <b>80</b> inside each closed space <b>3</b> against the front molding surface <b>201</b> before the surface skin on the resin material <b>80</b> which has filled the inside of the cavity <b>20</b>, it is possible to effectively prevent a state of strain such as a shrink from occurring on the front surface <b>801</b> corresponding to the partition standing wall <b>822</b> formation positions.

Therefore, according to the first embodiment, it is possible to effectively prevent a state of strain such as a shrink (a dimple formed on a surface) from occurring on a whole of the front surface <b>801</b> of the resin molded article <b>8</b>. Also, the heretofore described injection method and injection molding apparatus <b>1</b> are suitable particularly in carrying out an injection molding of a large-size or long resin molded article <b>8</b>.

The heretofore described injection molding method and injection molding apparatus <b>1</b> can be applied not only to the radiator grille, but to various resin molded articles obtained by carrying out a resin injection molding. Then, also when carrying out the injection molding of various resin molded articles, by previously providing a plurality of the gas inlets <b>4</b>A, <b>4</b>B, and <b>4</b>C along the passage direction L of the resin material <b>80</b> in the cavity <b>20</b>, it is possible to obtain the same working effect as the heretofore described one by carrying out the same operation as the heretofore described one.

Second Embodiment

Hereafter, a description will be given, along with the drawings, of a second embodiment related to a resin molded article manufacturing method and apparatus according to the invention.

In a resin molded article <b>8</b> manufacturing method and apparatus <b>101</b> of the second embodiment, as shown in <figref idrefs="DRAWINGS">FIG. 10</figref>, the resin molded article <b>108</b>, including a boss <b>182</b> of circular cross-section projected from a rear surface <b>902</b> of a plate-like body <b>181</b>, is manufactured.

As shown in <figref idrefs="DRAWINGS">FIG. 11</figref>, the manufacturing apparatus <b>101</b> includes a forming mold <b>102</b> having formed therein a body cavity <b>121</b> for molding the plate-like body <b>181</b> and a boss cavity <b>122</b> for molding the boss <b>182</b>. In the forming mold <b>102</b>, an inner gas nozzle <b>103</b> is provided inside an inner molding wall <b>123</b> forming an inner periphery <b>331</b> of the boss cavity <b>122</b>, and an outer gas nozzle <b>104</b> is provided in a rear molding surface <b>302</b> of the body cavity <b>121</b> for molding the rear surface <b>902</b> of the plate-like body <b>181</b>.

Then, in molding the resin molded article <b>108</b> using the manufacturing apparatus <b>101</b>, first, as shown in <figref idrefs="DRAWINGS">FIG. 12</figref>, an inside of the body cavity <b>121</b> and boss cavity <b>122</b> is filled with a resin material <b>180</b>.

Next, as shown in <figref idrefs="DRAWINGS">FIG. 13</figref>, by injecting a gas G from the outer gas nozzle <b>104</b> into an area between the rear molding surface <b>302</b> of the body cavity <b>121</b> and the resin material <b>180</b> which has filled the inside of the body cavity <b>121</b>, this resin material <b>180</b> is pressed against a front molding surface <b>301</b> of the body cavity <b>121</b> for molding a front surface <b>901</b> of the plate-like body <b>181</b>. Next, as shown in <figref idrefs="DRAWINGS">FIG. 14</figref>, by injecting the gas G from the inner gas nozzle <b>103</b> into an area between a leading end surface <b>333</b> of the inner molding surface <b>123</b> and the resin material <b>180</b> facing the leading end surface <b>333</b>, this resin material <b>180</b> is pressed against the front molding surface <b>301</b> of the body cavity <b>121</b>.

Hereafter, a detailed description will be given, along with <figref idrefs="DRAWINGS">FIGS. 10 to 15</figref>, of the resin molded article <b>108</b> manufacturing method and apparatus <b>101</b>.

In the resin molded article <b>108</b> manufacturing method of the second embodiment, by devising a timing of ejecting the gas G from the inner gas nozzle <b>103</b> and the outer gas nozzle <b>104</b>, a state of strain such as a shrink (a dimple formed on a surface) is effectively prevented from occurring on the front surface <b>901</b> of the resin molded article <b>108</b>.

The manufacturing apparatus <b>101</b> is for carrying out an injection molding of the resin molded article <b>108</b>. An injection pressure of the resin material <b>180</b> injected into the forming mold <b>102</b> is set at, for example, 30 to 50 MPa, and a heating temperature of the resin material <b>180</b> injected into the forming mold <b>102</b> is set at, for example, 200 to 250° C. Also, the gas G injected from the inner gas nozzle <b>103</b> and the outer pas nozzle <b>104</b> is a high pressure gas of 5 to 15 MPa.

Although not shown, the inner gas nozzle <b>103</b> and the outer gas nozzle <b>104</b> are configured in such a way as to carry out an ejection of the gas G and an interruption of the ejection by means of a valve which opens and closes a flow channel of the gas G. Also, a timing of ejecting the gas G from the inner gas nozzle <b>103</b> and the outer gas nozzle <b>104</b> can be controlled by control means such as a sequencer (a programmable controller).

Then, the control means in the manufacturing apparatus <b>101</b> is configured in such a way as to fill the inside of the body cavity <b>121</b> with the resin material <b>108</b>, after an elapse of a prescribed period of time, eject the gas G into the forming mold <b>102</b> from the outer gas nozzle <b>104</b>, and then, after a prescribed period of time has elapsed after the ejection, eject the gas G into the forming mold <b>102</b> from the inner gas nozzle <b>103</b>.

A timing of starting the injection of the gas G into the forming mold <b>102</b> from the outer gas nozzle <b>104</b> can be after the resin material <b>180</b> fills a whole of the body cavity <b>121</b> and boss cavity <b>122</b>. Also, a timing of starting the injection of the gas G into the forming mold <b>102</b> from the inner gas nozzle <b>103</b> can be, for example, after a surface portion of a molten resin, which makes contact with a surface of the forming mold <b>102</b>, starts to cure, and starts forming a surface skin (a cured portion). The timing of starting the injection of the gas G from the inner gas nozzle <b>103</b> can be, for example, when one to five seconds have elapsed after the start of the injection of the gas G from the outer gas nozzle <b>104</b>.

As shown in <figref idrefs="DRAWINGS">FIG. 11</figref>, the inner gas nozzle <b>103</b> includes a gap <b>343</b>A, through which the gas G is caused to pass, formed between a gas passage hole <b>341</b>A formed in the inner molding wall <b>123</b> forming the inner periphery <b>331</b> of the boss cavity <b>122</b> and a cylindrical body <b>342</b>A disposed in the gas passage hole <b>341</b>A. Also, the outer gas nozzle <b>104</b> includes a gap <b>343</b>B, through which the gas G is caused to pass, formed between a gas passage hole <b>341</b>B formed in the rear molding surface <b>302</b> of the body cavity <b>121</b> and a cylindrical body <b>342</b>B disposed in the gas passage hole <b>341</b>B.

The outer gas nozzle <b>104</b> of the second embodiment is formed in one portion in the body cavity <b>121</b>. In contrast, it is also possible that the outer gas nozzles <b>104</b> are formed in a plurality of portions of the body cavity <b>121</b>.

Also, as shown in <figref idrefs="DRAWINGS">FIG. 10</figref>, a projecting wall <b>911</b>, which projects from a rear surface <b>902</b> of the plate-like body <b>181</b> of the resin molded article <b>8</b> to be molded in the second embodiment, is formed around the plate-like body <b>181</b>. Then, a whole perimeter of the rear surface <b>902</b> of the plate-like body <b>181</b> is surrounded by the projecting wall <b>911</b>.

Also, as shown in <figref idrefs="DRAWINGS">FIG. 11</figref>, a projecting wall cavity <b>311</b> for molding the projecting wall <b>911</b> is continuously formed in the body cavity <b>121</b>.

As shown in <figref idrefs="DRAWINGS">FIG. 15</figref>, a rib cavity <b>125</b> for forming a strengthening rib <b>185</b> at a base of the boss <b>182</b> can be formed at a base of an outer periphery <b>332</b> of the boss cavity <b>122</b>. In this case, when filling the inside of the body cavity <b>121</b> and boss cavity <b>122</b> with the resin material <b>180</b>, this resin material <b>180</b> is also caused to fill an inside of the rib cavity <b>125</b> and, in a molded resin molded article <b>108</b>, the base of the boss <b>182</b> can be strengthened by the strengthening rib <b>185</b>.

In the second embodiment, in manufacturing the resin molded article <b>108</b>, a heated and molten resin material <b>180</b> is injected into the body cavity <b>121</b> from an injection portion (not shown) connected to the body cavity <b>121</b>. Then, as shown in <figref idrefs="DRAWINGS">FIG. 12</figref>, this resin material <b>180</b> fills not only the inside of the body cavity <b>121</b>, but also the inside of the projecting wall cavity <b>311</b>, as well as the inside of the boss cavity <b>122</b>.

To continue, as shown in <figref idrefs="DRAWINGS">FIG. 13</figref>, the gas G is injected from the outer gas nozzle <b>104</b> into the area between the rear molding surface <b>302</b> of the body cavity <b>121</b> and the resin material <b>180</b> which has filled the inside of the body cavity <b>121</b>. At this time, this gas G spreads from an installation position of the outer gas nozzle <b>104</b> to an area between the rear molding surface <b>302</b> of the body cavity <b>121</b> and the resin material <b>180</b> facing the rear molding surface <b>302</b>. Then, the gas G is prevented, by the resin material <b>180</b> having filled the inside of the body cavity <b>122</b>, from entering an area between the outer periphery <b>332</b> of the boss cavity <b>122</b> and the resin material <b>180</b> facing the outer periphery <b>332</b>. Also, the gas G is prevented, by the resin material <b>180</b> having filled an inside of the projecting wall cavity <b>311</b>, from entering up to the front molding surface <b>301</b> of the body cavity <b>121</b>.

In this way, as shown in the same figure, by the gas G injected into the rear molding surface <b>302</b> of the body cavity <b>121</b>, the resin material <b>180</b> inside the body cavity <b>121</b> is pressed against the front molding surface <b>301</b> of the body cavity <b>121</b>.

To continue, as shown in <figref idrefs="DRAWINGS">FIG. 14</figref>, after the prescribed period of time has elapsed after the start of the injection of the gas G from the outer gas nozzle <b>104</b>, the gas G is injected from the inner gas nozzle <b>103</b> into the area between the leading end surface <b>333</b> of the inner molding wall <b>123</b> and the resin material <b>180</b> facing the leading end surface <b>333</b>. By this time, a part of the resin material <b>180</b> facing the leading end surface <b>333</b> of the inner molding wall <b>123</b> has already started to cure, and started forming a surface skin. For that reason, the gas G injected from the inner gas nozzle <b>103</b>, without entering an inside of the resin material <b>180</b> inside the body cavity <b>121</b>, stays between the leading end surface <b>333</b> of the inner molding wall <b>123</b> and the surface skin on the resin material <b>180</b> facing the leading end surface <b>333</b>.

In the second embodiment, when injecting the gas G into the forming mold <b>102</b> from the inner gas nozzle <b>103</b>, the injection of the gas G into the forming mold <b>102</b> from the outer gas nozzle <b>104</b> is maintained.

In this way, as shown in the same figure, the resin material <b>180</b> portion facing the leading end surface <b>333</b> of the inner molding wall <b>123</b> is pressed against the front molding surface <b>301</b> of the body cavity <b>121</b> by the gas G injected into the leading end surface <b>333</b> of the inner molding wall <b>123</b>.

In this way, in the second embodiment, in a condition in which the resin material <b>180</b> positioned farther to an outer peripheral side than the boss cavity <b>122</b> is pressed against the front molding surface <b>301</b> of the body cavity <b>121</b>, the resin material <b>180</b> facing the leading end surface <b>333</b> of the inner molding wall <b>123</b> (the resin material <b>180</b> positioned on an inner peripheral side of the boss cavity <b>122</b>) can be pressed against the front molding surface <b>301</b> of the body cavity <b>121</b>.

Therefore, in the resin molded article <b>108</b> molded by the manufacturing method of the second embodiment, a state of strain such as a shrink can be effectively prevented from occurring on the front surface <b>901</b> corresponding to a whole of a boss <b>82</b> formation position.

Comparative Examples

In the comparative examples, a condition is shown in which a state of strain such as a shrink has occurred in molding the resin molded article <b>108</b>, as shown in <figref idrefs="DRAWINGS">FIGS. 16 and 17</figref>, in a case of not injecting the gas G into a forming mold <b>192</b>A from the outer gas nozzle <b>104</b>, but injecting the gas G into the forming mold <b>192</b>A from only the inner gas nozzle <b>103</b> (a comparative example 1) and, as shown in <figref idrefs="DRAWINGS">FIG. 18</figref>, in a case of injecting the gas G into a forming mold <b>192</b>B from only the outer gas nozzle <b>104</b>, and not injecting the gas G into the forming mold <b>192</b>B from the inner gas nozzle <b>103</b> (a comparative example 2).

Also, as shown in <figref idrefs="DRAWINGS">FIG. 16</figref>, in the case of the comparative example 1, in a molded resin molded article <b>109</b>A, although no shrink or the like has occurred in a position of the front surface <b>901</b> corresponding to a resin portion positioned on an inner peripheral side <b>921</b> of the boss <b>182</b>, a shrink H has occurred in a position of the front surface <b>901</b> corresponding to a resin portion positioned close to an outer peripheral side <b>922</b> of the boss <b>182</b>.

Also, as shown in <figref idrefs="DRAWINGS">FIG. 17</figref>, in the case of the comparative example 1, it is found that, in the event that the gas G is injected early into the forming mold <b>102</b> from the inner gas nozzle <b>103</b> (in a case in which the injection of the gas G is carried out before a surface skin is formed on the resin material <b>180</b> facing the leading end surface <b>333</b> of the inner molding wall <b>123</b>), the gas G enters an inside of a molten resin material <b>180</b>, and a hollow portion T is formed inside the resin material <b>108</b>.

Also, as shown in <figref idrefs="DRAWINGS">FIG. 18</figref>, in the case of the comparative example 2, in the molded resin molded article <b>108</b>, although no shrink or the like has occurred in the position of the front surface <b>901</b> corresponding to the resin portion positioned close to the outer peripheral side <b>922</b> of the boss <b>182</b>, the shrink H has occurred in the position of the front surface <b>901</b> corresponding to the resin portion positioned on the inner peripheral side <b>921</b> of the boss <b>182</b>.

It is found from these results that, in the resin molded article <b>108</b>, in order to effectively prevent a state of strain such as a shrink from occurring on the front surface <b>901</b> corresponding to the whole of the boss <b>182</b> formation position, it is necessary that the resin molded article <b>108</b> manufacturing method and apparatus <b>101</b> is configured as shown in the example described heretofore.